The use of imaging inspection apparatus of the above type is known, including those which utilize X-ray imaging. Such apparatus are used to inspect articles such as personal luggage of airplane travelers at airports for such undesirable items as explosives and drugs. One particularly successful example of such apparatus is that which utilizes what is referred to in the art as “X-ray Computer Tomography” (hereinafter also referred to as, simply, XCT). XCT apparatus are in wide use in the medical field for providing medical imaging such as patient body X-rays. XCT (often referred to in the medical profession simply as “CT scanning”) produces a cross sectional image from a grouping of attenuation measurements taken at different angles about an object such as a patient's chest or head, while the patient is maintained in a stationary position.
Some versions of the above apparatus have been modified to be more adaptable to taking images for non-medical purposes. In U.S. Pat. No. 5,367,552, issued Nov. 22, 1994, for example, a rotating XCT scanning unit is used which requires an object to remain stationary during scanning. This apparatus is designed for detecting concealed objects, such as explosives, drugs, or other contraband in a person's luggage. The apparatus uses scanning to identify concealed objects with a density corresponding to the density of target objects such as explosives or drugs. To reduce the amount of scanning required, a number of pre-scanning approaches are described in this patent. Based upon pre-scan data, selected locations for scanning are identified. The resulting scan data is utilized to automatically identify objects of interest, which identification is further verified through automatic analysis of such attributes as shape, texture, context, and X-ray diffraction. The objects of interest are then reconstructed and displayed on a computer monitor for visual analysis by the apparatus operator.
High speed scanning, such as that useful for scanning luggage of large numbers of travelers in a relatively shorter time period than provided by conventional stationary apparatus, requires that even further modifications be made. One such apparatus is described in U.S. Pat. No. 6,236,709, issued May 22, 2001, in which a continuous, XCT imaging system includes a conveyor which moves a closed package for being scanned along the conveyor past three spaced sensing stations. At each sensing station a plurality of X-ray sources each emit a fan beam in the same scan plane which passes through the package to a plurality of detectors opposite the X-ray sources. One scan is a vertical perpendicular scan plane relative to the direction of travel of the package along the conveyor belt and the remaining two scan planes are horizontal scan planes at right angles and transverse to the direction of travel. One horizontal scan plane is a left to right scan plane while the remaining scan plane is a right to left scan plane. Each detector provides multiple energy outputs for the same data point in a scan slice, and the detector outputs are stored until all three sensing stations have scanned the same cross sectional view of the package in three directions. Scans are sequentially taken as the package moves continuously through the sensing stations and scanned data corresponding to cross sectional views of the package is accumulated. The stored data is calibrated and normalized and then used in a Computer Tomographic algebraic reconstruction technique. This is described in this patent as a “multi-spectral CT reconstruction”, where the density of a reconstructed object is determined by the attenuation which it causes in the scanning X-rays while the atomic number of the object is determined from the multiple energy scan output. In a classifier, the density and atomic number are compared to a table containing density and atomic number identification values for specific objects to be located.
Accurate, rapid inspection of moving articles such as multiple luggage pieces, often having many different sizes and shapes, is, understandably, a relatively difficult task, as indicated by just some of the difficulties mentioned in some of the patents cited herein and elsewhere in the literature pertaining to this art with respect to articles in both stationary and moving positions. When utilizing many heat-generating devices such as X-ray sources, it is essential that these sources operate at the proper temperature. Otherwise, the devices may be subject to failure, which is costly in both replacement terms as well as apparatus shutdown. Maintaining these heat-generating devices at proper temperature is thus critical to assuring effective apparatus operation.
Attention is directed to the following U.S. Patents which describe various types of scanning apparatus (in addition to those cited in the patents above), some of which utilize some form of means to provide cooling for the apparatus.
In U.S. Pat. No. 6,778,635, issued Aug. 17, 2004, there is described an x-ray tube cooling system which utilizes a heat sink partially disposed within an evacuated housing of the x-ray tube and having a cooling block partially received within the bearing housing to absorb heat transmitted to the bearing assembly and bearing housing. Extended surfaces are disposed in a coolant chamber defined by the cooling block and a shell within which the cooling block is partially received. The shell defines a coolant chamber entrance and coolant chamber exit in fluid communication with the coolant chamber. The coolant chamber entrance and exit communicate with corresponding coolant inlet and outlet passageways, respectively, cooperatively defined by a pair of insulators which retain the heat sink in a predetermined orientation within an evacuated envelope of an x-ray device. A circulating coolant contacts the extended surfaces and thereby removes heat from various structures of the x-ray device.
In U.S. Pat. No. 6,714,626, issued Mar. 30, 2004, there is described an x-ray tube cooling assembly which includes an electron collector body coupled to an x-ray tube window and having a first coolant circuit. The coolant circuit includes a coolant inlet and a coolant outlet. The coolant outlet directs coolant at an x-ray tube window surface to impinge upon and cool the x-ray tube window. The coolant is reflected off the reflection surface to impinge upon and cool the x-ray tube window.
In U.S. Pat. No. 6,709,156, issued Mar. 23, 2004, there is described a cooling device for an X-ray source that is arranged in a gantry around a rotational axis. The device includes a ring-like heat exchanger that is positioned at the gantry and is thermally connected to the X-ray source. The cooling device is useable in a computed tomography apparatus having the X-ray source.
In U.S. Pat. No. 6,669,366, issued Dec. 30, 2003, there is described an X-ray examination apparatus in which the X-ray detector and the X-ray source are subject to keeping the temperature constant and to cooling by way of a common cooling “circuit”. A cooling medium of constant temperature is applied to the X-ray detector in order to make the detector operate at desired temperatures. The temperature of the cooling medium, increased a first time, allegedly performs cooling of the X-ray source. The heated cooling medium, after application to the X-ray detector, is applied to the X-ray source where a second exchange of heat takes place, so the X-ray source is cooled without utilizing an additional cooling circuit.
In U.S. Pat. No. 6,619,841, issued Sep. 16, 2003, there is described a fluid-cooled X-ray tube which includes a closed coolant “circuit” in which coolant circulates for the elimination of generated heat. In order to improve the cooling capacity, micro-capsules containing a phase-change material (PCM) are added to the coolant. In this arrangement, heat arising from the X-ray tube is intermediately stored in the PCM storage elements for a certain time span. Dependent on the selected material of the PCM and the amount of the PCM storage elements introduced into the coolant, the temperature of the coolant can be kept nearly constant over a specific time segment despite the heat arising from the tube during X-ray generation. Compared to conventional measures for cooling an X-ray tube, this patent mentions that the rise in temperature of the coolant is retarded by this arrangement, so that the X-ray radiator can be more highly stressed (loaded) over the same operating duration, or the operating duration of the X-radiator can be significantly lengthened given the same load. Described PCM materials for this purpose are paraffins whose melting temperatures lie between ninety and one hundred and twelve degrees Celsius. Mentioned alternatives to paraffin include fatty alcohols, fatty acids, hydrates of sodium carbonate, sodium acetate, calcium chloride and lithium magnesium nitrate.
In U.S. Pat. No. 6,529,579, issued Mar. 4, 2003, there is described a cooling system for high-powered X-ray tubes. The cooling system includes a reservoir containing liquid coolant, in which the high-powered X-ray tube is partially immersed. In general, the liquid coolant is cooled and then circulated through the reservoir by an external cooling unit. The cooling system also includes a shield structure attached to the vacuum enclosure of the X-ray tube and disposed substantially about the aperture portion of the vacuum enclosure, thereby defining a flow passage proximate the aperture portion. Liquid coolant supplied by the external cooling unit enters the flow passage by way of an inlet port in the shield structure. After passing through the flow passage and transferring heat out of the aperture portion, the liquid coolant is discharged through an outlet port in the shield structure and enters the reservoir to repeat the cycle.
In U.S. Pat. No. 6,496,564, issued Dec. 17, 2002, there is described an X-ray system with an X-ray “generating device” which includes an X-ray tube mounted in a casing holding a circulating, cooling medium. According to the description, the X-ray generating device includes a support mechanism mounted within the X-ray generating device in a manner for adjustably positioning, relative to the casing, the focal spot alignment path of generated X-rays. Additionally, the device includes a cooling mechanism having an inlet chamber for channeling the cooling medium within the support mechanism. Still further, a cooling stem may be positioned within the inlet chamber to increase the heat exchange surface area exposed to the cooling medium.
In U.S. Pat. No. 6,400,799, issued Jun. 4, 2002, there is described an x-ray tube cooling system which utilizes a shield structure connected between a cathode cylinder and an x-ray tube housing and disposed between the electron source and the target anode. The system uses a plurality of cooling fins to improve overall cooling of the x-ray tube and the shield so as to extend the life of the x-ray tube and related components. When immersed in a reservoir of coolant fluid, the fins facilitate improved heat transfer by convection from the shield to the to the coolant fluid. The cooling effect achieved with the cooling fins is further augmented by a convective cooling system provided by a plurality of passageways formed within the shield, which are used to provide a fluid path to the coolant. In particular, a cooling unit takes fluid from the reservoir, cools the fluid, and then circulates the cooled fluid through cooling passages. The coolant is then output from the passageway and directed over the cooling fins. In some embodiments, the passageways are oriented so as to provide a greater heat transfer rate in certain sections of the shield than in other sections.
U.S. Pat. No. 6,052,433, issued Apr. 18, 2000, describes an apparatus for performing dual-energy X-ray imaging using two-dimensional detectors. The apparatus consists of an X-ray source, a 2-dimensional X-ray detector, a beam selector, and a second 2-dimensional X-ray detector. The subject is located between the X-ray source and first detector. The beam selector prevents primary X-rays from reaching selected locations of the second (rear) detector. A pair of primary dual-energy images is obtained at the rear detector. Using a dual-energy data decomposition method, a low-resolution primary X-ray first detector image is calculated, from which a high-resolution primary dual-energy image pair is calculated. In addition, the data decomposition method is used to calculate a pair of high-spatial-resolution material composition images.
U.S. Pat. No. 6,018,562, issued Jan. 25, 2000, describes an apparatus for automatic recognition and identification of concealed objects and features thereof, such as contraband in baggage or defects in articles of manufacture. The apparatus uses multiple energy X-ray scanning to identify targets having a spectral response corresponding to a known response of targets of interest. Detection sensitivity for both automatic detection and manual inspection are improved through the multiple-energy, multi-spectral technique. Multi-channel processing is used to achieve high throughput capability. Target identification may be verified through further analysis of such attributes as shape, texture, and context of the scan data. The apparatus uses a statistical analysis to predict the confidence level of a particular target identification. A radiograph, CT image, or both may be reconstructed and displayed on a computer monitor for visual analysis by the apparatus operator. Finally, the apparatus may receive and store input from the operator for use in subsequent target identification.
U.S. Pat. No. 5,991,358, issued Nov. 23, 1999, describes a data acquisition system for use in a CT scanner which consists of an analog-to-digital converter for generating digital signals in response to analog signals representative of projection data taken at a relatively constant sampling rate. The apparatus also uses an interpolation filter for generating projection data for a plurality of predetermined projection angles as a function of the digital signals irrespective of the sampling rate. This patent references a known system which includes an array of individual detectors disposed as a single row in the shape of an arc of a circle having a center of curvature at a certain point, referred to as the “focal spot”, where the radiation emanates from the X-ray source. The X-ray source and the array of detectors in this known system are positioned so that the X-ray paths between the source and each of the detectors all lie in the same plane (hereinafter the “rotation plane” or “scanning plane”) which is normal to the rotation axis of the disk. Since the X-ray paths originate from what is substantially a point source and extend at different angles to the detectors, the X-ray paths form a “fan beam.” The X-rays incident on a single detector at a measuring interval during a scan are commonly referred to as a “ray”, and each detector generates an analog output signal indicative of the intensity of its corresponding ray. Since each ray is partially attenuated by all the mass in its path, the analog output signal generated by each detector is representative of an integral of the density of all the mass disposed between that detector and the X-ray source (i.e., the density of the mass lying in the detector's corresponding ray path) for that measuring interval.
U.S. Pat. No. 5,629,966, issued May 13, 1997, describes a real time radiographic test system which consists of a protective housing and a conveyor for conveying articles to be tested through the housing. A real time radiographic test instrument is located in the housing for performing a real time radiographic test on the article. The test instrument includes X-ray equipment disposed for directing an X-ray beam within the housing in a direction which does not intersect the conveyor. An article-handling actuator is located in the housing for repositioning an article from the conveyor to a position in registry with the X-ray beam, for maintaining the article in registry with the X-ray beam while the real time radiographic test is performed on the article and thereafter returning the article to the conveyor. The article-handling actuator and the X-ray equipment are designed such that each article to be tested is positioned substantially identically relative to the X-ray beam.
U.S. Pat. No. 5,583,904, issued Dec. 10, 1996, describes a laminographic system that allows generation of high speed and high resolution X-ray laminographs by using a continuous scan method with two or more linear detectors and one or more collimated X-ray sources. Discrete X-ray images, with different viewing angles, are generated by each detector. The discrete X-ray images are then combined by a computer to generate laminographic images of different planes in the object under test, or analyzed in such a manner to derive useful data about the object under test. This system does not require any motion of the source or detectors, but simply a coordinated linear motion of the object under test. Higher speed is achieved over conventional laminography systems due to the continuous nature of the scan, and due to the ability to generate any plane of data in the object under test without having to re-image the object.
U.S. Pat. No. 5,524,133, issued Jun. 24, 1996, describes an X-ray analysis device for determining the mean atomic number of a material mass by locating a broad band X-ray source on one side of a testing station and on the other, a detector, comprising a target having X-ray detectors positioned adjacent thereto. One of the detectors is positioned and adapted to receive X-rays scattered by the detector target in a generally rearward direction and the other detector is positioned and adapted to detect forwardly propagating X-rays scattered off axis typically by more than thirty degrees, due to so-called “Compton scatter.” Each of the X-ray detectors provides signals proportional to the number of X-ray photons incident thereon. The apparatus further includes means responsive to the two detector outputs which form a ratio of the number of photons detected by the two detectors and forms a numerical value thereof. A look-up table containing mean atomic numbers for given numerical ratios for different materials is used, as is a means for determining from the look-up table the atomic number corresponding to the numerical ratio obtained from the outputs of the two detectors. The atomic number is provided as an output signal.
U.S. Pat. No. 5,483,569, issued Jan. 9, 1996, describes an inspection system for inspecting objects with “penetrating radiation” having a conveyor with first and second portions which are separated by a gap. Illumination by this radiation is provided in a scanning plane which is located in the gap, and the system may be used for the inspection of thin objects. Additionally, the illumination may be arranged in the inspection of normal size objects, e.g., suitcases or cargo boxes, so that it does not include a ray which is perpendicular to any face of the object. Further, the relative orientation of the scanning plane and the faces of the object may be arranged so that the illumination does not include a ray which is parallel to any face of the object. A scanning configuration wherein the illumination does not include a ray which is perpendicular or parallel to any face of an object having parallel faces, for example, a rectangular solid, results in a display projection of the object which appears to be three dimensional.
U.S. Pat. No. 5,259,012, issued Nov. 2, 1993, describes a system which enables multiple locations within an object to be imaged without mechanical movement of the object. The object is interposed between a rotating X-ray source and a synchronized rotating detector. A focal plane within the object is imaged onto the detector so that a cross-sectional image of the object is produced. The X-ray source is produced by deflecting an electron beam onto a target anode. The target anode emits X-ray radiation where the electrons are incident upon the target. The electron beam is produced by an electron gun which includes X and Y deflection coils for deflecting the electron beam in the X and Y directions. Deflection voltage signals are applied to the X and Y deflection coils, and cause the X-ray source to rotate in a circular trace path. An additional DC voltage applied to the X or Y deflection coil will cause the circular path traced by the X-ray source to shift in the X or Y direction by a distance proportional to the magnitude of the DC voltage. This causes a different field of view, which is displaced in the X or Y direction from the previously imaged region, to be imaged. Changes in the radius of the X-ray source path result in a change in the Z level of the imaged focal plane.
U.S. Pat. No. 5,026,983, issued Jun. 25, 1991, describes an apparatus for examining food products for undesired ingredients by means of laser irradiation. A laser beam scans the food products according to a predetermined pattern. Variations in the intensity of the laser beam passing through the food products indicate the presence of undesired ingredients. This method is carried out by an apparatus which comprises two parabolic mirrors, a laser emitting a laser beam so as to originate from the focus of one of the mirrors and a detection means positioned in the focus of the other mirror. The food products are moved between the mirrors by conveyor belts.
U.S. Pat. No. 5,020,086, issued May 28, 1991, describes a situation where an object is scanned by an X-ray beam from a circular position on a target resulting from the electron beam being scanned in a circle by appropriate control signals from a beam controller and applied to the deflection coils of a microfocus X-ray tube. Tomosynthesis is accomplished by the well-known method of in-register combination of a series of digital X-ray images produced by X-ray beams emanating from different locations. This is achieved by positioning an X-ray source at multiple points on a circle around a central axis. This system eliminates some mechanical motion in that the detector does not have to rotate. However, practical limitations of pixel size and resolution tend to limit this system to inspection of items with small fields of view. Additionally, the system still requires an X, Y table to position the object under the field of view.
The above patents and co-pending applications are incorporated herein by reference.
The present invention defines a new and unique inspection method which assures that effective cooling of the scanning devices is assured. Such cooling is accomplished for a number of scanning devices in a new and unique manner representing a significant improvement over cooling methods for apparatus such as described above. It is believed that such a method would constitute a significant advancement in the art.